As a homeowner that burns wood as a primary source of heat in the winter, I am always looking for a more efficient approach when firing my stove. My goal has been to employ outside air to feed my fire for several years, and so I completed the following research to find out what other wood burning experts have to say about the subject. Here is what I found.
Should I feed my fire with outside air directly into the firebox? There are conflicting responses to this question. My answer is yes; you should, in most instances. I will explain further in the article.
There are some circumstances where I would advise against feeding the fire with outside air, and I will clarify these later. First, I will give my reasons and instances where I would feed the fire with direct outside air.
How Wood Stoves Work
Fire in any form requires three elements to burn. Fuel, heat, and air. Since the mid-1980s, when wood stove became popular (mainly due to the “energy shortage”), wood stoves changed the way we burned wood in homes for heat. Before then, most homes had fireplaces, and generally, they were used primarily as a gathering place, not a true heat source. They would burn a large quantity of wood in a short time, and most of the heat (about 90%) went up the chimney. The fire pulled large amounts of air from the room where the fireplace was to feed the fire and released it out of the chimney. This air had to come from somewhere, and that was from any leaky window, door, or floor in the home.
A few clever inventors (welders) found that a stove could be constructed of steel, with a sealed door, and the air into the stove would control the fire. By increasing or reducing the air, the wood burner would become hotter or cooler. The efficiency of the stove was increased by 500%. This still meant that 40-50% of the heat went up the chimney, but that was better than the 90% from a fireplace. Less heat was being wasted, and more heat stayed in the home.
The stove was still drawing air from the room to feed the fire but so much less. Is this problem resolvable? The air has to come from somewhere. Just like the fireplace, the air is being drawn from outside the house through leaky spaces in floors or windows. Why not stop pulling the air through the room.
Outside Air
To resolve this, my intent is to introduce outside air directly into the firebox. Most stoves today are capable of installing an outside air kit. Some areas, by code, require outside air to feed the fire.
By adding the outside air kit, the stove will not be pulling cold air from the outside, through the room, and then into the fire. This alone will allow the home to be warmer by not changing the home to negative air pressure. Negative air pressure is when air is escaping the area (home or room) at a stronger rate than air is entering.
As long as you still can control the air that is input to the stove firebox, you can control the fire. You may have to pay closer attention to the wind speed (that is an issue with every stove even without outside air feeding the fire) as it may impact the stove differently.
Feeding the fire with outside air may also help your home be more humid in the winter. Dry air pulled from outside by the wood burner will give the impression that a wood burner “dries” out the house. The outside air being pulled in is more of an issue that the wood burner being a “dry heat.”
You will also not be pulling air from a crawl space if you have one. By doing this, you may be pulling in damp, moldy air, and that is never desirable.
My last argument on the side of using outside air to feed the fire is the use of outside air on 90%+ efficient furnaces. These natural gas and LPG furnaces draw their air for combustion from outside the home. They do it efficiently, and it is a standard feature on all furnaces today.